Chemical process and composition

ABSTRACT

The invention relates to a process for production of hydrogen peroxide according to the anthraquinone process including alternate hydrogenation and oxidation of one or more quinones selected from anthraquinones and/or tetrahydro anthraquinones in a working solution comprising at least one quinone solvent and at least one hydroquinone solvent, wherein said at least one quinone solvent comprises isodurene in an amount from 15 to 100 wt %. The invention also relates to a composition useful as a working solution at production of hydrogen peroxide.

[0001] The present invention relates to a process for production ofhydrogen peroxide according to the anthraquinone process, wherein theworking solution comprises a certain mixture of solvents. The inventionalso concerns a composition comprising such a mixture of solvents thatis useful as a working solution at production of hydrogen peroxide.

[0002] The most common process for production of hydrogen peroxide isthe anthraquinone process. In this process quinones selected fromoptionally substituted anthraquinones and/or tetrahydro anthraquinonesdissolved in a suitable organic solvent mixture, a so called workingsolution, are hydrogenated to form the corresponding hydroquinones. Thehydroquinones are then oxidised back to quinones with oxygen (usuallyair) with simultaneous formation of hydrogen peroxide, which then can beextracted with water while the quinones are returned with the workingsolution to the hydrogenation step.

[0003] The anthraquinone process is described extensively in theliterature, for example in Kirk-Othmer, “Encyclopedia of ChemicalTechnology”, 4^(th) Ed., 1993, Vol. 13, pp. 961-995.

[0004] For the process to work properly, it is necessary to use asolvent mixture for the working solution in which both quinones andhydroquinones are soluble. Therefore, the solvent mixture in the workingsolution normally comprises one or more quinone solvents and one or morehydroquinone solvents.

[0005] The problem of finding suitable solvents for the working solutionhas been addressed in, for example, U.S. Pat. Nos. 3,328,128, 4,800,073and 4,800,074, and GB patent 1524883.

[0006] In many cases, the production capacity in a plant is limited bythe amount of quinones available for hydrogenation in the workingsolution or the amount of hydroquinones that can be formed withoutprecipitation thereof. This problem has been found to be of particularimportance when the amount of tetrahydro anthraquinones in the workingsolution is high.

[0007] Thus, there is a demand for a working solution based on a solventcombination with improved solubility of both quinones and hydroquinones,particularly of tetrahydro anthraquinones. Furthermore, it is desirableto provide a working solution with comparatively low density, whichfacilitates the phase separation at an extraction step performed afterthe hydrogenation and oxidation steps.

[0008] It has now been found possible to provide a working solutionfulfilling these demands by selecting a certain combination of solvents.

[0009] Thus, the invention concerns a process for production of hydrogenperoxide according to the anthraquinone process including alternatehydrogenation and oxidation of one or more quinones selected fromanthraquinones and/or tetrahydro anthraquinones in a working solutioncomprising at least one quinone solvent and at least one hydroquinonesolvent, wherein said at least one quinone solvent comprises isodurene(1,2,3,5-tetramethylbenzene) in an amount from 15 to 100 wt %,preferably from about 20 to about 80 wt %, most preferably from about 25to about 70 wt %.

[0010] Most preferably the at least one quinone solvent referred toabove substantially consists of one or more essentially non-polarorganic solvents, preferably hydrocarbons, while the at least onehydroquinone solvent referred to above most preferably substantiallyconsists of one or more polar organic solvents, suitably essentiallynon-soluble in water and preferably selected from alcohols, ureas,amides, caprolactams, esters, phosphorus containing substances andpyrrolidones.

[0011] It has been found that when the proportion of isodurene comparedto other optional quinone solvents is high, the solubility of quinonesis improved to such an extent that it is possible to decrease the totalamount of quinone solvents in the working solution and instead increasethe amount of hydroquinone solvents, and thereby increase the solubilityof both quinones and hydroquinones.

[0012] In addition to isodurene, the at least one quinone solventsuitably comprises durene (1,2,4,5-tetramethylbenzene), wherein thetotal amount of isodurene and durene suitably constitutes from about 30to about 100 wt %, preferably from about 35 to about 80 wt % of thetotal amount of quinone solvents. In order to avoid precipitation ofdurene the content thereof should not be too high, preferably notexceeding about 25 wt %, most preferably not exceeding about 20 wt % ofthe total amount of quinone solvents. The weight ratio isodurene todurene in the working solution is preferably from about 1.5:1 to about5:1, most preferably from about 2:1 to about 4:1.

[0013] The at least one quinone solvent may also comprise other suitablyessentially non-polar hydrocarbons, preferably selected from one or morearomatic, aliphatic or naphthenic hydrocarbons, of which aromatichydrocarbons are most preferred. Particularly suitable quinone solventsinclude benzene, alkylated or polyalkylated benzenes such astert-butylbenzene or trimethyl benzene, alkylated toluene or naphthalenesuch as tert-butyltoluene or methylnaphthalene.

[0014] The preferred total content of quinone solvents and consequentlyalso the content of isodurene used in the entire working solutiondepends on which hydroquinone solvent(s) that are used. In most cases,the suitable content of quinone solvents is from about 25 to about 65 wt%, preferably from about 40 to about 60 wt % of the entire workingsolution. In most cases, the weight ratio quinone solvents tohydroquinone solvents suitably is from about 0.6 to about 4, preferablyfrom about 1.5 to about 3. The suitable content of isodurene normally isfrom about 8 to about 52 wt %, preferably from about 11 to about 42 wt %of the entire working solution.

[0015] The working solution comprises at least one and preferably atleast two hydroquinone solvents, suitably selected from polar organicsolvents, which, however, preferably should be essentially non-solublein water. Suitable hydroquinone solvents may be selected from alcohols,ureas, amides, caprolactams, esters, phosphorus containing substancesand pyrrolidones, and include alkyl phosphates (e.g. trioctylphosphate), alkyl phosphonates, alkylcyclohexanol esters, N,N-dialkylcarbonamides, tetraalkyl ureas (e.g. tetrabutyl urea),N-alkyl-2-pyrrolidones and high boiling alcohols, preferably with 8-9carbon atoms (e.g. di-isobutyl carbinol). Preferred hydroquinonesolvents are selected from alkyl phosphates, tetraalkyl ureas, cyclicurea derivatives and alkyl-substituted caprolactams. One group ofpreferred hydroquinone solvents are described in the U.S. Pat. Nos.4,800,073 and 4,800,074 and include alkyl-substituted caprolactams suchas octyl caprolactam and cyclic urea derivatives such asN,N′-dialkyl-substituted alkylenurea. Other preferred hydroquinonesolvents include di-isobutyl carbinol and tetrabutyl urea, which areadvantageous in the sense that they have low density.

[0016] The content of hydroquinone solvents in the working solution ispreferably from about 15 to about 48 wt %, most preferably from about 18to about 35 wt %.

[0017] The anthraquinones and tetrahydro anthraquinones in the workingsolution to be hydrogenated are preferably alkyl substituted, mostpreferably with only one alkyl group, suitably at the 2-position.Preferred alkyl substituents include amyl such as 2-tert-amyl or2-iso-sec-amyl, ethyl, tert-butyl and 2-hexenyl, and it is particularlypreferred that at least ethyl substituted anthraquinones and/ortetrahydro anthraquinones are included. Preferably the working solutionto be hydrogenated include a mixture of different alkyl substitutedanthraquinones and tetrahydro anthraquinones, more preferably a mixtureof ethyl and at least one other alkyl substituted, most preferably amylsubstituted anthraquinone and/or tetrahydro anthraquinone. Preferablyfrom about 50 to about 100 mole %, most preferably from about 60 toabout 90 mole % of the anthraquinones and the tetrahydro anthraquinonesare substituted with one ethyl group. It is also preferred that up toabout 50 mole %, most preferably from about 10 to about 40 mole % of theanthraquinones and the tetrahydro anthraquinones are substituted withone amyl group.

[0018] It has been found favourable to operate at high amounts oftetrahydro anthraquinones compared to anthraquinones, as it then ispossible to achieve high degree of hydrogenation and low losses ofactive quinones to degradation products. Suitably the molar ratio oftetrahydro anthraquinones to anthraquinones in the working solution tobe hydrogenated exceeds 1:1 and is preferably from about 2:1 to about50:1, most preferably from about 3:1 to about 20:1. In some cases it maybe appropriate to operate at a molar ratio only up to about 9:1, but itis also possible to use working solutions almost free fromanthraquinones.

[0019] The molar ratio of tetrahydro anthraquinones to alkylanthraquinones in a mature working solution (a working solution used forhydrogen peroxide production during at least six months) is suitably inthe same magnitude for the anthraquinones substituted with differentgroups. The molar ratio for each group differ preferably less than witha factor of about 2.5, most preferably less than with a factor of about1.7.

[0020] The tetrahydro anthraquinones are normally mainly made up ofβ-tetrahydro anthraquinones, but also some α-tetrahydro anthraquinonesmay be present.

[0021] Besides the direct or indirect hydrogenation to hydroquinones,many secondary reactions take place. For example, theanthrahydroquinones can react further to tetrahydro anthrahydroquinones,which in the oxidation step is converted to tetrahydro anthraquinones,the content of which thus will increase in the working solution. Thismeans that when the process of the invention is started up, the initialworking solution may contain no or only small amounts of tetrahydroanthraquinones, as they will form automatically during the course ofoperation. As soon as the desirable concentrations of anthraquinones andtetrahydro anthraquinones have been reached, at least a portion of theworking solution is then normally treated to dehydrogenate tetrahydroanthraquinones back to anthraquinones.

[0022] It also occurs direct or indirect formation of unwantedby-products, such as epoxides, octahydro anthraquinones, oxanthrones,anthrones and dianthrones. Some of these compounds, like epoxides can beconverted back to anthraquinones, while others, like dianthrones,constitute an irreversible loss of active working solution. It has beenfound that the formation of undesired by-products can be minimised ifthe molar ratio of tetrahydro anthraquinones to anthraquinones ismaintained within the above specified range.

[0023] The high amounts of isodurene in the working solution renders itpossible to dissolve high amounts of ethyl substituted tetrahydroanthraquinone, which has lower density than, for example, the highlysoluble amyl substituted tetrahydro anthraquinone. It is then possibleto combine high concentration of quinones available for hydrogenation inthe working solution with low density, thus increasing the productioncapacity of hydrogen peroxide per volume working solution. The totalamount of anthraquinones and tetrahydro anthraquinones in the workingsolution to be hydrogenated is preferably from about 15 to about 28 wt%, most preferably from about 17 to about 25 wt %, while the densitymeasured at 20° C., preferably is from about 910 to about 980 kg/m³,most preferably from about 930 to about 970 kg/m³.

[0024] The hydrogenation step is normally performed by contacting theworking solution with hydrogen gas in the presence of a catalyst at atemperature from about 0 to about 100° C., preferably from about 40 toabout 75° C., and at an absolute pressure from about 100 to about 1500kPa, preferably from about 200 to about 600 kPa. The degree ofhydrogenation (as moles hydroquinones per m³ working solution) issuitably from about 350 to about 800, preferably from about 400 to about650.

[0025] The active catalyst may, for example, be a metal selected fromany of nickel, palladium, platinum, rhodium, ruthenium, gold, silver, ormixtures thereof. Preferred metals are palladium, platinum and gold, ofwhich palladium or mixtures comprising at least 50 wt % palladium areparticularly preferred. The active catalyst may be in free form, e.g.palladium black suspended in the working solution, or be deposited on asolid support such as particles used in the form of a slurry or a fixedbed. However, it is particularly preferred to use a catalyst in the formof an active metal on a monolithic support, for example, as described inU.S. Pat. Nos. 4,552,748 and 5,063,043. Preferred support materials areselected from silica or aluminium oxide.

[0026] Before or after the hydrogenation step, at least a portion of theworking solution is preferably regenerated in one or several steps toremove water, to keep the desired ratio of tetrahydro anthraquinones toanthraquinones, to convert some undesired by-products from thehydrogenation or the oxidation steps back to active components, and toremove other undesired by-products. The regeneration may includefiltration, evaporation of water, and treatment with a porous adsorbentand catalyst based on aluminium oxide.

[0027] Other steps in the overall process of producing hydrogenperoxide, such as oxidation with oxygen or air and extraction withwater, may be performed in conventional manner as described in theliterature.

[0028] The invention further concerns a composition useful as a workingsolution at production of hydrogen peroxide with the anthraquinoneprocess. The composition comprises one or more anthraquinones and/or oneor more tetrahydro anthraquinones dissolved in at least one quinonesolvent, and at least one hydroquinone solvent, wherein said at leastone quinone solvent comprises isodurene in an amount from 15 to 100 wt%, preferably from about 20 to about 80 wt %, most preferably from about25 to about 70 wt %. Regarding optional and preferred features of thecomposition, the above description of the process is referred to.

[0029] The invention will now further be described in connection withthe following Examples, which, however, not should be interpreted aslimiting the scope of the invention.

EXAMPLE 1

[0030] The solubility of β-tetrahydro ethyl anthraquinone was measuredin two different pure quinone solvents: Solvent: Regular mixtureIsodurene Technical grade aromatic (mixture comprising 69 wt %hydrocarbons isodurene, 22 wt % durene), 9 (mainly C₁₀ + C₉) wt % otherC₁₀ aromatic (Shellsol ™ AB) hydrocarbons Solubility at 20° C. 115g/liter 180 g/liter

EXAMPLE 2

[0031] Two different mature working solutions, A (comparative) and B(the invention), were tested in an anthraquinone process, the solutionsthus also containing normal degradation products. Both solutionscomprised tetrabutyl urea as hydroquinone solvent and 2-ethyl and 2-amylsubstituted anthraquinones and tetrahydro anthraquinones (the molarratio 2-ethyl to 2-amyl exceeded 1:1 and was maintained constant). Themolar ratio tetrahydro anthraquinones to anthraquinones exceeded 3:1.

[0032] The main difference between the working solutions was that inSolution A the quinone solvent was made up of ShellSol™ AB, a regularmixture of aromatic hydrocarbon with mainly C₁₀ and C₉ alkyl-benzene(about 85%), while in Solution B the quinone solvent instead was made upof 40 wt % Shellsol™ AB mixed with 60 wt % of isodurene (Technical gradecomprising about 69% isodurene, about 22% durene and about 9 wt % otherC₁₀ aromatic hydrocarbons).

[0033] In both cases the total content of tetrahydro anthraquinones andanthraquinones were kept as high as possible to reach highconcentrations of hydrogen peroxide in the working solution. However,precipitation β-tetrahydro ethyl anthraquinone and/or its hydroquinoneform in the working solution was a limiting factor.

[0034] More data are shown in the table below: Working solution: A BIsodurene as wt% of quinone solvent 10% 45% Isodurene as wt% of workingsolution  5% 21% Durene as wt% of quinone solvent  7% 16% Tetrabutylurea as wt% of working 22% 25% solution Density of working solution (20°C.) 950 kg/m³ 960 kg/m³ Total content of tetrahydro 122% relative Aanthraquinones and anthraquinones (about 18-23 wt %) Hydrogen peroxidelimit in working 125% relative A solution

[0035] It was thus possible to operate working solution B with a higherproduction capacity than solution A.

1. A process for production of hydrogen peroxide according to theanthraquinone process including alternate hydrogenation and oxidation ofone or more quinones selected from the group consisting ofanthraquinones and tetrahydro anthraquinones, in a working solutioncomprising at least one quinone solvent and at least one hydroquinonesolvent, wherein said at least one quinone solvent comprises isodurenein an amount from 15 to 100 wt %.
 2. A process as claimed in claim 1,wherein said at least one quinone solvent comprises from about 20 toabout 80 wt % of isodurene.
 3. A process as claimed in claim 1, whereinthe working solution comprises from about 25 to about 70 wt % ofisodurene.
 4. A process as claimed in claim 1, wherein said at least onequinone solvent additionally comprises durene and the total amount ofisodurene and durene constitutes from about 30 to about 100 wt % of thequinone solvents.
 5. A process as claimed in claim 1, wherein said atleast one quinone solvent additionally comprises durene and the contentof durene does not exceed about 25 wt % of total amount of quinonesolvents.
 6. A process as claimed in claim 4, wherein the weight ratioisodurene to durene in the working solution is from about 1.5:1 to about5:1.
 7. A process as claimed in claim 1, wherein said at least onehydroquinone solvent comprises one or more compounds selected from thegroup consisting of di-isobutyl carbinol and tetrabutyl urea.
 8. Aprocess as claimed in claim 1, wherein the molar ratio of tetrahydroanthraquinones to anthraquinones in the working solution to behydrogenated exceeds 1:1.
 9. A process as claimed in claim 8, whereinthe molar ratio of tetrahydro anthraquinones to anthraquinones in theworking solution to be hydrogenated is from about 2:1 to about 50:1. 10.A process as claimed in claim 1, wherein from about 50 to about 100 mole% of the anthraquinones and the tetrahydro anthraquinones aresubstituted with one ethyl group.
 11. A process as claimed in claim 1,wherein the density, measured at 20° C., is from about 910 to about 980kg/m³.
 12. A process for production of hydrogen peroxide according tothe anthraquinone process including alternate hydrogenation andoxidation of one or more quinones selected from the group consisting ofanthraquinones and tetrahydro anthraquinones, in a working solutioncomprising at least one quinone solvent and at least one hydroquinonesolvent, wherein said at least one quinone solvent comprises isodurenein an amount from 15 to 100 wt % and additionally durene in an amountnot exceeding about 25 wt % of total amount of quinone solvents, thetotal amount of isodurene and durene constitutes from about 30 to about100 wt % of the quinone solvents
 13. A process as claimed in claim 12,wherein said at least one quinone solvent comprises from about 20 toabout 80 wt % of isodurene.
 14. A process as claimed in claim 12,wherein the working solution comprises from about 25 to about 70 wt % ofisodurene.
 15. A process as claimed in claim 12, wherein the weightratio isodurene to durene in the working solution is from about 1.5:1 toabout 5:1.
 16. A process as claimed in claim 12, wherein said at leastone hydroquinone solvent comprises one or more compounds selected fromthe group consisting of di-isobutyl carbinol and tetrabutyl urea.
 17. Aprocess as claimed in claim 12, wherein the molar ratio of tetrahydroanthraquinones to anthraquinones in the working solution to behydrogenated exceeds 1:1.
 18. A process as claimed in claim 17, whereinthe molar ratio of tetrahydro anthraquinones to anthraquinones in theworking solution to be hydrogenated is from about 2:1 to about 50:1. 19.A process as claimed in claim 12, wherein from about 50 to about 100mole % of the anthraquinones and the tetrahydro anthraquinones aresubstituted with one ethyl group.
 20. Composition useful as a workingsolution at production of hydrogen peroxide with the anthraquinoneprocess comprising one or more quinones selected from the groupconsisting of anthraquinones and tetrahydro anthraquinones, dissolved inat least one quinone solvent and at least one hydroquinone solvent,wherein said at least one quinone solvent comprises isodurene in anamount from 15 to 100 wt %.